Mobile antenna springs and SWR question

[WRHS218]

I should know this but if I ever did I don't remember... Does adding a spring to a mobile antenna on a NMO mount change the SWR? Years and years ago I added a spring to a 2m antenna. It was on the roof of a Toyota FJ which is already pretty tall. The spring eliminated the bent and broken antennas I had experienced on trails up to that point. I didn't have an SWR meter back then so never tested the antenna before and after the spring was added. Somebody mentioned springs in a recent post but I didn't want to derail that post.

[kidphc]

It can help and hurt.

Most springs are calculate into the length of the radiating (active) length of the antenna.

For instance, the comet 2x4sr (think this post is the one you are referring to) is about the same length as the section that is removed to install it. It would not affect anything. You can actually tune the antenna by unlocking the allen grub screws and increase or decrease the length of the antenna smidgen. But because of it being a collimeter design it can be a bit tricky to do right.

Which is unlike cb antenna steel whips. Which are technically too short, most commercial whips are about 102". By adding the 6" spring to the base it brings it closer to the natural resonance length. Give or take with spring it's 108". Resonance is about 108-112" (true 1/4 length) for 11mhz/cb.

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[nokones]

You definitely want to recheck the VSWRs if it wasn't tuned/check with the spring.